Many processes are already known for manufacturing copper and its alloys with very low concentrations of impurities, e.g. less than 50 ppm, and/or with very low oxygen contents, e.g. less than 5 ppm. Similar processes are also used in industry for other metals (e.g. in the case of aluminum and iron).
The objective of the various technologies in accordance with the prior art usually involves the following:
the removal of reaction products, and/or impurities, and/or materials comprising slag, and/or the individual/miscellaneous elements that are present in the liquid metal.
The following are known in this regard in order to achieve the desired refining effects: the use of e.g. filters, the provision of dwell times for settling processes, treatment via additions that react with the impurities, the use of physical separating processes such as e.g. scavenging, the application of a vacuum, etc. in one or more steps in combination with the above technologies, or in the form of the pertinent individual application of these technologies.
These processes have become known and have found their widest application in the treatment of aluminum and steel along with their alloys, whereas they are used only in part in the copper industry.
Poling with tree trunks and reducing gases have generally been used from time immemorial for removing the oxygen content of copper during its manufacture. The addition of reducing elements, such as e.g. phosphorus and lithium or boron in the form of e.g. starting alloys, is also known. Use is also made of filters, slag sumps, vacuum chambers/vacuum furnaces and/or settling times in order to purify the metal.
In the case of copper, all the processes that are listed above are applied and exploited in a widespread manner in order to decrease its very high concentrations of impurities and/or oxygen (e.g. in excess of 200-2000 ppm). Likewise, it is known that deoxidizing agents, such as e.g. phosphorus, can also be used simultaneously as an alloying element for achieving particular material properties.
In order to manufacture very pure copper materials, use is made almost generally of electrolytically refined copper (cathodes) as the basic material whose level of impurities in the case of stock market registered versions lies below 100 ppm as a result of the preceding steps in the refining procedure (thermal and chemical).
In the case of the additional thermal processing steps via melting and casting that then always follow on, the concentration of impurities and/or the concentration of oxygen is decreased further as a result of additional process steps and, in part, via the technologies that are listed above, or, as the case may be, the contamination level, which is caused by melting and casting or which is still present, is eliminated.
Thus, for example, electrical melting down of copper cathodes is used in the form of a discontinuous or continuous standard process for decreasing the oxygen content to below 5 to 15 ppm, whereby, in some processes, the cathodes are additionally heated to 950° C. beforehand via gas burners in order to increase melting efficiency or to remove adhering/included impurities.
Melting down then takes place in an electric furnace, which is provided with wood charcoal and/or a reducing protective gas, which is largely free from hydrogen, or, preferably, in induction furnaces. Transfer of the liquid copper then takes place via a channel, which, if necessary, is electrically heated and which is also flooded with a reducing/protective gas, and thence into a holding furnace/buffer furnace/settling furnace that is also usually constructed in the form of an induction furnace, and that is again covered with wood charcoal, and/or that it is flooded with a reducing/protective gas. After leaving this furnace, the melt is transferred via a channel, which is also electrically heated and which is flooded with a reducing/protective gas, and thence into an electrically heated tundish that is also covered with wood charcoal, and/or that is flooded with a reducing/protective gas. On its way from the tundish, the liquid metal arrives, usually via a ceramic valve, which is installed in the bottom, in the ingot mold that is, in part, also covered with a reducing/protective gas and/or with e.g. carbon black, whereby the metal solidifies continuously in the ingot mold and is drawn off continuously or discontinuously.
This standard process that has been described is essentially based on a reducing atmosphere in the furnace and the channels and, in particular, on the large exchange surface between the metal and the reducing/protective gas inside the transfer system in the channels, and also on the long dwell time inside the furnace.
Processes are also known within, and in addition to, this standard process that, in part, conduct the above process steps without, or only in part with, a reducing/protective gas. Processes are also known that merely seek to achieve low oxygen contents via long dwell times of the liquid metal in an induction furnace under a covering of wood charcoal.
Moreover, processes are known that additionally undertake the treatment of the liquid metal via a vacuum and/or, additionally, the above standard process or, as the case may be, their modifications.
It is already known from DE-OS 36 40 753 that a mixture comprising a gaseous hydrocarbon and an inert gas can be blown into a copper melt in order to remove oxygen from the copper melt. This blowing in procedure can take place by using a porous clay brick, or by using a special nozzle.
An additional process and a device are known from DE-OS 20 19 538 for de-gassing and purifying metal melts. In particular, a procedure is described for decreasing the proportion of oxygen in a copper melt when using porous flushing plugs from which an inert gas emerges that ascends into the copper melt. Reducing or oxidizing gases can be added to the inert gas.
The devices and processes in accordance with the prior art are not suitable to an adequate extent for decreasing the oxygen content of the metal melt to a proportion of less than 5 ppm in a reproducible manner and at an adequate production speed together with appropriate costs for carrying out the process.